A reflection absorption infrared spectroscopy and density-functional theory investigation of methanol dehydrogenation on Rh(111)V alloy surfaces.

The dehydrogenation reaction of methanol on a Rh(111) surface, a Rh(111)V subsurface alloy, and on a Rh(111)V islands surface has been studied by thermal-desorption spectroscopy, reflection absorption infrared spectroscopy, and density-functional theory calculations. The full monolayer of methanol forms a structure with a special geometry with methanol rows, where two neighboring molecules have different oxygen-rhodium distances. They are close enough to form a H-bonded bilayer structure, with such a configuration, where every second methanol C-O bond is perpendicular to the surface on both Rh(111) and on the Rh(111)V subsurface alloy. The Rh(111)V subsurface alloy is slightly more reactive than the Rh(111) surface which is due to the changes in the electronic structure of the surface leading to slightly different methanol species on the surface. The Rh(111)V islands surface is the most reactive surface which is due to a new reaction mechanism that involves a methanol species stabilized up to about 245 K, partial opening of the methanol C-O bond, and dissociation of the product carbon monoxide. The latter two reactions also lead to a deactivation of the Rh(111)V islands surface.

Differentiation of substrate and nonsubstrate inhibitors of the high-affinity, sodium-dependent glutamate transporters.

Within the mammalian central nervous system, the efficient removal of L-glutamate from the extracellular space by excitatory amino acid transporters (EAATs) has been postulated to contribute to signal termination, the recycling of transmitter, and the maintenance of L-glutamate at concentrations below those that are excitotoxic. The development of potent and selective inhibitors of the EAATs has contributed greatly to the understanding of the functional roles of these transporters. In the present study, we use a library of conformationally constrained glutamate analogs to address two key issues: the differentiation of substrates from nontransportable inhibitors and the comparison of the pharmacological profile of synaptosomal uptake with those of the individual EAAT clones. We demonstrate that the process of transporter-mediated heteroexchange can be exploited in synaptosomes to rapidly distinguish transportable from nontransportable inhibitors. Using this approach, we demonstrate that 2,4-methanopyrrolidine-2,4-dicarboxylate, cis-1-aminocyclobutane-1,3-dicarboxylate, and L-trans-2, 4-pyrrolidine dicarboxylate act as substrates for the rat forebrain synaptosomal glutamate uptake system. In contrast, L-anti-endo-3, 4-methanopyrrolidine-3,4-dicarboxylate, L-trans-2,3-pyrrolidine dicarboxylate, and dihydrokainate proved to be competitive inhibitors of D-[(3)H]aspartate uptake that exhibited little or no activity as substrates. When these same compounds were characterized for substrate activity by recording currents in voltage-clamped Xenopus laevis oocytes expressing the human transporter clones EAAT1, EAAT2, or EAAT3, it was found that the pharmacological profile of the synaptosomal system exhibited the greatest similarity with the EAAT2 subtype, a transporter believed to be expressed primarily on glial cells.

[Medicamentous prevention of symptomatic paroxysmal atrial fibrillation/flutter onset. Goals and design of the SOPAT Study. Executive committee of the investigators representing trial physicians]. / Die medikamentöse Anfallsprophylaxe bei symptomatischem paroxysmalem Vorhofflimmern/-flattern. Ziele und Design der SOPAT-Studie. Investigators in Vertretung der Prüfärzte.

The indication to treat symptomatic paroxysmal atrial fibrillation is discussed controversely. Successful medical treatment may result in the reduction of symptoms by improving hemodynamics in a reduction of thromboembolic events. However, several antiarrhythmic drugs are also known to increase the risk of proarrhythmic events. A randomized, double-blind, and placebo-controlled multicenter trial with 1000 patients to be recruited was designed to compare the effects of two antiarrhythmic drugs frequently used in Germany for the treatment of atrial fibrillation, Sotalol and the fixed combination of chinidin and verapamil (Cordichin). Patients with symptomatic paroxysmal atrial fibrillation/atrial flutter will be observed for a period of one year. The occurrence of paroxysmal atrial fibrillation is documented by transtelephonic ECG monitoring. Patients with document an ECG once daily, and recording is mandatory in case of symptoms. ECGs are transmitted to a central data base for analysis. This clinical trial is designed to answer the following questions: (1) What is the average rate of spontaneous events of symptomatic atrial fibrillation? (2) Is it possible to reduce the frequency of symptomatic events by chronic antiarrhythmic drug administration? (3) What is the long-term frequency for the occurrence of severe side-effects under antiarrhythmic medication? The primary endpoint is defined as the time to first recurrence of symptomatic arrhythmia after reaching steady-state plasma concentrations of the study medication. The trial started in November 1997 and is planned to be finished by the end of 1999.

[Medicamentous prevention after electric cardioversion of chronic atrial fibrillation. Goals and design of the PAFAC Study]. / Die medikamentöse Prophylaxe nach elektronischer Kardioversion von chronischem Vorhofflimmern. Ziele und Design der PAFAC-Studie.

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia. However, despite manifold publications reflecting numerous clinical trials about treatment of AF, the management of this arrhythmia is still under controversial discussion, in daily clinical work as well as in research. The present study concentrates on three major questions: 1. How frequent are recurrences of AF in long-term follow-up? Most of the previous studies used the occurrence of symptoms as a surrogate parameter for recurrences of AF, despite the expected high rate of asymptomatic relapses. In the present study a daily transtelephonic ECG transmission enables a rhythm monitoring independent of symptoms. 2. Is the frequency of AF recurrences significantly reduced by antiarrhythmic medication? A direct comparison of class I and III antiarrhythmic drugs, which still are most frequently used for this indication, and of placebo will answer this question. 3. How safe is the long-term treatment for the prevention of AF recurrences with special respect to proarrhythmic effects? The daily transtelephonic ECG transmission enables a quantitative and qualitative monitoring of tachy- and bradyarrhythmias independent of symptoms. Additionally, the daily analysis of ECG measures may detect parameters predicting subsequent life threatening arrhythmias. The study design provides a prospective, randomised, double-blind, placebo controlled, multicenter parallel group comparison. In Germany and in the Czech Republic about 90 hospitals will include 900 patients with documented chronic AF, age 18 to 80 years, if they are eligible for electrical cardioversion without concomitant antiarrhythmic drug therapy and if they are anticoagulated for at least three weeks prior to inclusion. Neither the size of the left atrium nor the duration of chronic AF are exclusion criteria. A few hours after successful electrical cardioversion the patients are randomised either to sotalol (2 x 160 mg) or quinidine + verapamil (3 x 160 mg + 3 x 80 mg) or placebo. Starting at the day after cardioversion, the patient is asked to record and transmit electrocardiograms of one minute duration at least once a day using his personal transtelephonic ECG recording unit (Tele-ECG recorder, credit card size), in case of symptoms as often as necessary. The ECGs can be transmitted at any time by any regular phone without additional equipment using a toll free number. A custom made, computer based, fully automated receiving centre is handling the patient calls interactively with voice control, including a voice recording of the patient's symptoms. The ECG tracings and the patient's voice messages are subsequently computer based analysed by experienced technicians. All ECG measures are stored in a database. In case of AF recurrence, any other relevant arrhythmia or additional abnormalities (e.g. QT prolongation) the correspondent hospital is immediately informed by fax. In case of AF recurrence, a subsequent Holter recording discriminates in paroxysmal and permanent AF. Study medication is ended if either permanent AF or the third episode of paroxysmal AF are detected or after 12 months of follow-up. Regular follow-up visits are performed monthly. Major endpoints are the time to first recurrence of AF or the time to death, secondary parameters are the number of AF recurrences, the time to end of medication and AF related symptoms. The recruitment started in the last days of 1996. Until the end of June 1998, 424 patients have been randomised. It is expected to end recruitment in spring 1999 and to close the study in spring 2000. Final results will be available in summer 2000.

Nontransportable inhibitors attenuate reversal of glutamate uptake in synaptosomes following a metabolic insult.

Na+-dependent, high-affinity glutamate transporters in the central nervous system are generally credited with regulating extracellular levels of L-glutamate and maintaining concentrations below those that would induce excitotoxic injury. Under pathological conditions, however, it has been suggested that these same transporters may contribute to excitotoxic injury by serving as sites of efflux for cellular L-glutamate. In this study, we examine the efflux of [3H]D-aspartate from synaptosomes in response to both alternative substrates (i.e., heteroexchange), such as L-glutamate, and a metabolic insult (5 mM potassium cyanide and 1 mM iodoacetate). Exposure of synaptosomes containing [3H]D-aspartate to either L-glutamate or metabolic inhibitors increased the efflux of the radiolabeled substrate to over 200% of control values. Two previously identified competitive transport inhibitors (L-trans-2, 3-pyrrolidine dicarboxylate and dihydrokainate) failed to stimulate [3H]D-aspartate efflux but did inhibit glutamate-mediated heteroexchange, consistent with the action of nontransportable inhibitors. These compounds also attenuated the efflux of [3H]D-aspartate from synaptosomes exposed to the metabolic inhibitors. These results add further strength to the model of central nervous system injury-induced efflux of L-glutamate through its high-affinity transporters and identify a novel strategy to attenuate this process.

Structural determinants of substrates and inhibitors: probing glutamate transporters with 2,4-methanopyrrolidine-2,4-dicarboxylate.

Using an intramolecular [2 + 2] photocyclization, 2,4-methanopyrrolidine-2,4-dicarboxylate was prepared as a conformationally locked analogue of glutamate. This compound, in combination with two other pyrrolidine dicarboxylates, has been used to define the structural elements that differentiate substrate and nonsubstrate inhibitors of a high-affinity, sodium-dependent glutamate transporter.

L-trans-2,3-pyrrolidine dicarboxylate: characterization of a novel excitotoxin.

This study investigated the in vitro and in vivo excitotoxic properties of a novel conformationally constrained analogue of L-glutamate, L-trans-2,3-pyrrolidine dicarboxylate (L-trans-2,3-PDC). When tested for excitotoxic activity in rat cortical cultures, L-trans-2,3-PDC mimicked the action of NMDA in both acute (30 min) and chronic (24 h) exposure paradigms. This neurotoxicity was attenuated by co-addition of MK-801 (10 microM). Microinjections of L-trans-2,3-PDC into the dorsal hippocampus of male rats also induced a selective pattern of pathology indicative of an NMDA receptor excitotoxin. In contrast to the equipotency observed in vitro, 100 nmol of L-trans-2,3-PDC were needed to produce cellular damage comparable to that induced by 25 nmol of NMDA. Consistent with an action at NMDA receptors, L-trans-2,3-PDC-induced damage could be significantly reduced by co-administration of MK-801 (3 mg/kg i.p.), but not by NBQX (25 nmol). In radioligand binding assays L-trans-2,3-PDC inhibited the binding of 3H-L-glutamate to NMDA receptors (IC50 1 microM), although it also exhibited some cross reactivity with KA and AMPA receptors. L-trans-2,3-PDC was also identified as a competitive inhibitor (Ki = 33 microM) of 3H-D-aspartate uptake into rat forebrain synaptosomes. In contrast to the action of a transported substrate, such as L-glutamate, L-trans-2,3-PDC did not exchange with 3H-D-aspartate that had been previously loaded into the synaptosomes.

The concept of fractals in the pharmaceutical sciences.

An old problem is sometimes better understood when it is viewed from a new perspective than by investigating it repeatedly with classical methods. Such a new perspective is provided by the concept of fractals. Briefly, this term defines a spread class of geometric shapes, whose subunits replicate the structure of the larger unit in accordance with the formalization of the idea of self-similarity. This concept was introduced by Mandel-brot in respond to the need for a more sophisticated explanation of numerous phenomena commonly encountered in nature. In this review we will provide a short introduction into the concept of fractals and a concise overview of those studies where fractal geometry has been employed so far in pharmaceutical research. We believe that a review of the most recent findings in the application of fractal geometry to problems encountered in the pharmaceutical sciences might be helpful also to those people who are involved in the search for novel drug substances, as well as in the investigation of their performance in vitro and in vivo. A few suggestions will be made where this concept probably could be helpful in the future and instructions will be given on how the fractal dimension of rugged objects can be estimated practically.

Pharmacokinetics and organ distribution of liposome-encapsulated L-carnitine in rats.

The pharmacokinetics and organ distribution of 3H-L-carnitine (CAS 541-15-1) were investigated in rats following direct intravenous administration of the drug substance and administration of the drug encapsulated in liposomes, respectively. The retention in the blood system of carnitine in liposomes, was significantly higher, namely up to 300% as compared to the standard administration. The half-life of distribution t1/2 alpha to 0.68 h (+154%), the terminal half-life t1/2 beta to 7.94 h (+140%), whereas the total clearance decreased by 400% as compared with the standard carnitine administration. Carnitine, in the novel dosage form, accumulated to a higher extent in the liver (156%) and spleen (336%), while the concentration in lung (52%), heart (55%) and muscle tissue (54%) decreased markedly relative to the standard. The novel dosage form is stable in vitro (t1/2 4 degree C = 187 days) as well as in vivo and, thus, may be successfully used in the therapy of carnitine deficiency, for instance in patients with renal failure or liver disease.

The yeast test: an alternative method for the testing of acute toxicity of drug substances and environmental chemicals.

A novel testing procedure has been developed with the aim to replace the traditional LD50 test in vertebrates by a method using a non-pain sensitive organism. Several years of practical experience have proven this method to be a rather quick, simple, inexpensive, outstandingly well reproducible and reliable experimental technique which yields an estimate for the acute toxicity of drugs, environmental chemicals, solvents, food additives, pesticides, industrial and waste products, and the like. The model is equivalent to the customary LD50 test in mice, rats and other laboratory animals. The yeast test, as it has been briefly named, employs ordinary yeast (Saccharomyces cerevisiae) in a thermostatized incubation mixture with nutrients and trace elements. The test substance is added to this mixture by increasing concentration, and the effect upon the growth rate of the yeast cells is monitored at 30, 90, 150 and 210 min after beginning the experiment by counting the cell number, either in a simple counting chamber under the microscope or, more conveniently, by using an electronic Coulter counter. The effect is expressed as percent growth of the cells in relation to the untreated control. Evaluation of the experimental data leads to a general toxicity parameter, the mean inhibitory concentration or IC50 value of the compound under test. Hitherto it was found that the IC50 values of approx. 160 common drugs and other chemicals correlate well with the known LD50 values found in animals with the same substances.

[The anti-ischemic effect of gallopamil-retard in comparison with nifedipine-retard in stable angina pectoris]. / Antiischämische Wirkung von Gallopamil retard im Vergleich zu Nifedipin retard bei stabiler Angina pectoris.

To assess the antiischemic efficacy of slow-release (SR) gallopamil, 100 mg b.i.d., versus slow-release (SR) nifedipine, 20 mg b.i.d., 24 patients with chronic stable angina underwent symptom-limited bicycle ergometer exercise stress tests in a randomized, placebo-controlled, double-blind, cross-over protocol. Both medications caused a significant reduction in anginal attack frequency and nitroglycerin consumption as compared to placebo; similarly, exercise tolerance was augmented in association with a considerable reduction in ischemia-induced ST-segment depression. The antiischemic effect of gallopamil (SR) was marginally superior to that of nifedipine (SR). Since the incidence of adverse effects was also less with gallopamil (SR) this drug exhibited a more favorable risk-benefit ratio relative to nifedipine (SR).

[The yeast test: an alternative method for determination of acute toxicity of drugs and environmental chemicals]. / Der Hefe-Test: Eine Alternativmethode zur Bestimmung der akuten Toxizität von Arzneistoffen und Umweltchemikalien.

Starting point for this study was the urgent need for replacement of the contemporary mode of acute toxicity testing of chemicals in vertebrates (LD50-test) by an experimental model with equal power that can be performed on non-pain sensitive matter. For this purpose, a testing procedure ought to be developed using a non-pathogenic microorganism as testing object that is available at any time, easy to cultivate, and in its indicative power equivalent to the LD50 test in mice, rats, and other laboratory animals. Such an organism has been found with ordinary yeast (baker's yeast, brewer's yeast, Saccharomyces cerevisiae) which can always be obtained in good quality. This procedure (shortly denominated as 'yeast test' offers several advantages: It is rather simple, inexpensive, outstandingly well reproducible, and it can be carried out conveniently also in routine experiments. The results correlate well with those furnished by the customary methods of acute toxicity testing.

[Computer simulation of blood level profiles. Drug liberation from two sustained-release preparations and computer simulation of single- and multiple-dose pharmacokinetics]. / Computersimulation von Blutspiegelprofilen. Wirkstoffliberation aus zwei Retardpräparaten und Computer-Simulation der Ein- und Mehrdosen-Pharmakokinetik.

A series of computer programs (BASIC) is introduced for the evaluation of in vitro dissolution data as well as for the calculation of pharmacokinetic parameters and for blood level curve fitting to the respective in vitro data. Furthermore, programs are offered for the simulation of blood level profiles under variable conditions. In order to demonstrate the practical use of these programs, the expected blood level profiles following the administration of two commercial sustained-release dosage forms containing the drug pentoxifylline have been compared.